The electrolytic conductivity detector was originally reported by Piringer and Pascalau in the Journal of Chromatography, volume 8, p. 410, 1962. By combusting a sample in a furnace containing a CuO catalyst, that sample was converted to carbon dioxide. The carbon dioxide was subsequently dissolved in deionized water and the conductivity of the water was constantly monitored. Similarly, Coulson extended this theory of operation to include the selective detection of halogen, sulfur, and nitrogen containing compounds as described in the Journal of Gas Chromatography, volume 73, p. 19, 1972. Further improvements have been claimed in: Journal of Chromatography, volume 73, p. 19, 1972; Journal of Chromatographic Science, volume 12, p. 152, 1972; Analytical Chemistry, volume 46, p. 755, 1974; Analytic Chemistry, volume 46, p. 755, 1974; Analytic Chemistry, volume 47, p. 367, 1975; U.S. Pat. No. 3,934,193, 1976; U.S. Pat. No. 4,032,296, 1977; NTIS pp. 250 451/256, 1976; U.S. Pat. No. 4,555,383, 1985, U.S. Pat. No. 4,649,124, 1987. Electrolytic conductivity detectors in general are reviewed by Selucky in Chromatographia, volume 5, p. 359, 1972, and specifically for nitrogen detection by Hall in CRC Critical Reviews in Analytical Chemistry, p. 323, 1978.
The importance of proper solvent pH of electrolytic conductivity detectors has been documented by Patchett in Journal of Chromatographic Science, volume 8, p. 155, 1969; Coulson in the Journal of Gas Chromatography, p. 258, 1966; and Pape, et al. in The Journal of Chromatography, volume 134, p. 1, 1977. If, in the nitrogen mode, the pH of the electrolyte is below 7, a decrease in response, "w" shaped peaks, and negative peaks have been observed. For this reason, Selucy in Chromatographia, volume 5, p. 323, 1978, and Jones, et al. in the Journal of Chromatography, volume 73, p. 19, 1972, have claimed that the pH of the solvent should be maintained between 7.0 and 8.0.
Maintenance of solvent pH for the nitrogen mode is usually accomplished through mixed bed resins. Most often, a strong mixed resin bed is preceded by a small amount of a strong base resin of the amine or hydroxyl type. Pape, Rodgers, and Flynn, however, in The Journal of Chromatography, volume 134, p. 1, 1977, have suggested the introduction of nitrogen into the reaction gas stream by means of a mixing manifold as a means of controlling pH.
Mixed bed resins, while controlling the pH to some extent, optimizing peak shape and sensitivity, suffer in actual operation. The final pH of the solvent with these types of systems is highly dependent on flow rate through the bed. This property is used to advantage by Pape, Rodgers, and Flynn in The Journal of Chromatography, volume 134, pp. 1-24, 1977, who use this dependency as the controlling factor in pH adjustment. Having a set flow rate through the resin bed, however, reduces the flexibility in application to differing cell designs and operational techniques. Furthermore, the flow rate needed to maintain a specific pH is not constant over an extended period of time. Cox and Tanaka, in Analytical Chemistry, volume 57, p. 385, 1985, have shown that the ion exchange rate of a resin bed depends on both the ionic content of the incoming solvent and the degree of ionic depletion of the resin bed.
In addition, the two component resin system is harder to prepare than a single component resin system.